Rock bolt

ABSTRACT

An anchor device which includes a pipe ( 16 ), an elongate member ( 18 ) which is partly inside the pipe and which has an end ( 20 ) which protrudes from the pipe ( 16 ), and a restraining component ( 22 ) which is engaged with the protruding end ( 20 ). The pipe ( 16 ) and the elongate member ( 18 ) are shaped with a plurality of deformations along their respective lengths such that the elongate member ( 18 ) can only be withdrawn from the tubular member ( 16 ) by further deforming the elongate member ( 18 ).

CROSS REFERENCE TO RELATED APPLICATION

This application is the National Stage filing under 35 U.S.C. 371 ofInternational Application No. PCT/ZA03/00032, filed Feb. 25, 2003, andclaims priority of South African Patent Application 2002/1531, filedFeb. 25, 2002.

BACKGROUND OF THE INVENTION

This invention relates to an anchor device.

As used herein the expression “anchor device” designates a load carryingdevice which is capable of yielding in a controlled manner when the loadon the device increases above a predetermined limit.

Without being restrictive in any way an anchor device, as defined, maybe used as a rock bolt to reinforce a rock face or as a reinforcingelement in a concrete structure such as a bridge or building.

SUMMARY OF INVENTION

According to a first aspect of the invention there is provided a methodof forming an anchor device which includes the steps of:

-   (a) locating an elongate member at least partly within a tubular    member; and-   (b) simultaneously deforming the elongate member and the tubular    member at least at one location whereby withdrawal of the elongate    member from the tubular member is inhibited.

At least a portion of the elongate member and of the tubular member maybe deformed into a substantially sinusoidal shape.

The elongate member and the tubular member may be deformed at each of aplurality of locations which are spaced from each other in alongitudinal direction of the elongate member.

The method may include the step of securing a restraining component toan end of the elongate member which extends from the tubular member.

The tubular member may be at least one pipe and the elongate member maybe selected from the following: a rod and a cable.

The invention also provides an anchor device which includes a tubularmember, and an elongate member at least partly inside the tubularmember, the tubular member and the elongate member being shaped, in acomplementary manner, at least at one location whereby withdrawal of theelongate member from the tubular member is inhibited.

The arrangement may be such that the elongate member can only bewithdrawn from the tubular member by deforming the elongate member.

The anchor device may include a restraining component at an end of theelongate member which protrudes from the tubular member.

The elongate member may be any appropriate element or elements and, forexample, may be selected from a rod and a cable.

BRIEF DESCRIPTION OF THE DRAWING

The invention is further described by way of example with reference tothe accompanying drawing wherein:

FIG. 1 depicts, from the side and in cross section, an anchor deviceaccording to the invention; and

FIG. 2 is an enlarged detail view of the circled portion of FIG. 1.

DESCRIPTION OF PREFERRED EMBODIMENT

The accompanying drawing illustrates from the side and in cross sectionan anchor device 10, according to the invention, installed in a hole 12which is formed in a rock face 14.

The anchor device includes an elongate tubular member 16 which is in thenature of a thin wall steel pipe and an elongate load bearing member 18which is inserted into the pipe with one end 20 protruding from thepipe.

The member 18 may be a steel rod or a cable.

A restraining component 22 is secured to the protruding end 20 and bearsagainst a load distributing washer 24 which in turn acts against asurface of the rock face 14 which surrounds the hole 12.

The restraining device varies according to the nature of the elongatemember 18. For example if the elongate member is a steel rod then theprotruding end 20 may be threaded and the restraining component 22,which is then in the nature of a nut, is threadedly engaged with the end20. Alternatively if the member 18 is a cable or is formed from a numberof wires then the restraining component 22 may be in the nature of a lugor ferrule which is crimped onto the protruding end in situ at aninstallation site.

The anchor device 10 is formed, under factory conditions, by insertingthe elongate member 18 into the pipe 16 when the pipe is of a regularshape ie. is not deformed. The pipe, which encloses the elongate memberover a substantial portion of the length of the elongate member, isplaced in a suitable press and is deformed in one or a plurality ofsteps into the shape shown in the drawing. The deformed pipe has peaksand troughs with a generally smooth transition between each peak andadjacent trough thereby imparting to the pipe an overall generallysinusoidal shape.

The undulations or sinusoidal peaks are spaced apart by a distance 26which varies according to requirement.

The hole 12 is formed in the rock face using any appropriate techniqueknown in the art and the anchor device 10 is placed in the hole with thepipe 16 embedded in grout or other settable material 28 which fills thehole. The settable material is normally injected into the hole using anysuitable placement apparatus after the pipe has been inserted into thehole.

If the restraining component 22 is a nut then the washer and the nut areengaged with the protruding end 20 after the settable material isinjected into the hole through its mouth. On the other hand if therestraining component is in the nature of a lug or similar device whichis applied under factory conditions to the protruding end then the loaddistribution washer 24 may initially be displaced slightly from the rockface 14 to allow the settable material to be injected into the holethrough its mouth or, alternatively, the washer 24 may have an apertureor passage formed through it and the settable material may be injectedthrough the aperture or passage into the hole 12.

Ideally, once the material 28 has set, the component 22 is advancedalong the member 18 to prestress the member. This may however not bepossible if the component is crimped under factory conditions to the end20. It is preferable therefore to attach the component to the end 20 insitu, at the installation location.

When the anchor device is embedded in the settable material, thematerial, whether grout, resin or of a different type, bonds to theexterior surface of the pipe which is thereby held firmly in position.

If there is movement of the rock face relatively to the bulk of the rockin which the hole 12 is formed then the load which is carried by themember 18 increases. The member 18 is therefore placed under increasingtensile stress. The rock face 14 can only move however when the loadcarried by the member 18 is so high that the element is deformed throughthe sinusoidal passage which is defined by the pipe 16. It is evidentthat the point at which yielding takes place is dependent on a number offactors including the material from which the elongate member is made,the dimensions and shape of the member, the clearance between the memberand the inner wall of the pipe, and the number, depth and spacing of theformations in the pipe and the member.

The elongate member slides through the pipe by deforming as it passesthrough the undulations to provide a controlled yielding action with thepipe remaining behind and fully embedded in the settable material. Anappropriate lubricant may be applied to the elongate member, before itis inserted into the pipe. This helps to ensure that a smooth slidingaction takes place as yielding occurs, particularly if the yield rate ishigh ie. when the member 18 moves very rapidly, for example during aseismic event.

The length of the anchor device may be substantial. This makes theanchor device suitable for use in reinforced concrete applications forexample in bridges and structures. With this type of application themember 18 will generally be a cable or comprise a plurality of hightensile winds which may be helically twisted, at least slightly. Theinstallation and operation of the anchor device, in a reinforcedconcrete application, for all practical purposes, are the same as whathas been described hereinbefore with reference to the use of the anchordevice in a body of rock except that the device is cast in position.

The pipe 16 is rigid and if the anchor device is made to a substantiallength it may be difficult to install the device particularly in anunderground situation or in a location in which there is limited space.To impart a degree of flexibility to the anchor then, as is shown moreclearly in the inset drawing, the member 18 may be a cable and the pipe16 may comprise a plurality of relatively smaller lengths 16A, 16B, . .. which are separated from each other along the length of the cable bymeans of suitable spacers 30, which may be made from a flexible plasticsmaterial. Each individual pipe length is sinusoidally deformed, with thecable inside, in the manner which has been described and is fixed inposition when it is embedded in the settable material. However, beforeinstallation, it is possible to bend or flex the anchor device, at leastto a limited degree, by bending one pipe section to a limited extentrelatively to an adjacent pipe section. The use of the spacers does notadversely affect the strength of the anchor device nor the yieldingaction thereof.

The invention claimed is:
 1. A method of forming a rock anchor devicewhich includes the steps of: (a) locating an elongate substantiallystraight load bearing member partly within a substantially rigid tubularmember which encloses one end of the elongate member over a portion ofthe length of the elongate member; (b) securing a restraining componentof the anchor device to an opposite end of the elongate member whichextends from the tubular member at a location that is outside thetubular member; and (c) simultaneously deforming the elongate member andthe tubular member at each of a plurality of locations to formrespective deformations which are spaced from each other in alongitudinal direction of the elongate member so that withdrawal of theelongate member from the tubular member results in further deformationof the elongate member within the tubular member to provide a controlledyielding action; and wherein: the step of locating includes placing theelongated member in the tubular member such that they are capable ofsliding movement relative to one another in the longitudinal direction;and said step of simultaneously deforming produces complementarydeformations that cause the elongate member to no longer be straight andinhibit but do not destroy the relative sliding movement capability. 2.A method according to claim 1 wherein at least a portion of the elongatemember and a portion of the tubular member are simultaneously deformedto produce complementary deformations having a substantially sinusoidalshape.
 3. A method according to claim 1 wherein the elongate member andthe tubular member are simultaneously deformed to have a plurality ofpeaks and troughs.
 4. A method according to claim 1 wherein the tubularmember includes at least one pipe.
 5. A method according to claim 1wherein the elongate member is one of a rod and a cable.
 6. A methodaccording to claim 1 wherein the complementary deformations cause theportion of the elongate member enclosed by the tubular member to have asubstantially sinusoidal shape in a longitudinal direction.
 7. An anchordevice which includes a rigid tubular member, and an elongate loadbearing member having one end inside the tubular member, which enclosesthe elongate member over a portion of the length of the elongate member,and a restraining component that is secured to an opposite end of theelongate member extending from the tubular member and at a location thatis outside the tubular member, with the tubular member and the enclosedportion of the elongate member both being deformed, in a complementarymanner, at each of a plurality of locations to form respectivedeformations which are spaced from each other in a longitudinaldirection of the elongate member and with the shape of the complementarydeformations being such that withdrawal of the elongate member from thetubular member is inhibited to provide a controlled sliding and yieldingaction; and wherein a lubricant is provided on the elongate memberinside the tubular member.
 8. An anchor device according to claim 4wherein the deformed portion of the elongate member extends in alongitudinal direction with a substantially sinusoidal shape.
 9. Ananchor device according to claim 7 wherein the end of the tubular memberadjacent said one end of said elongate member is closed.
 10. An anchordevice which includes a tubular member, and an elongate load bearingmember having one end inside the tubular member, which encloses theelongate member over a portion of the length of the elongate member, anda restraining component that is secured to an opposite end of theelongate member extending from the tubular member and at a location thatis outside the tubular member, with the tubular member and the enclosedportion of the elongate member both being deformed, in a complementarymanner, at each of a plurality of locations to form deformations whichare spaced from each other in a longitudinal direction of the elongatemember and with the shape of the complementary deformations being suchthat withdrawal of the elongate member from the tubular member isinhibited to provide a controlled sliding and yielding action; andwherein the tubular member includes a plurality of pipes through whichthe elongate member passes.
 11. An anchor device according to claim 10wherein adjacent pipes are separated by flexible spacers.
 12. An anchordevice according to claim 10 wherein the deformed portion of theelongate member extends in a longitudinal direction with a substantiallysinusoidal shape.
 13. An anchor device which includes a rigid tubularmember, and an elongate toad bearing member having one end inside thetubular member that includes a plurality of pipes through which theelongate member passes, with the tubular member and the elongate memberbeing shaped, in a complementary manner, at each of a plurality oflocations to form deformations which are spaced from each other in alongitudinal direction of the elongate member so that withdrawal of theelongate member from the tubular member is inhibited while providing acontrolled sliding and yielding action when the tubular member isanchored and a predetermined load is applied to the elongate member; andwherein adjacent pipes are separated by flexible spacers.
 14. An anchordevice according to claim 13 wherein the deformed portion of theelongate member extends in a longitudinal direction with a substantiallysinusoidal shape.
 15. An anchor device which includes a tubular member,and an elongate load bearing member having one end inside the tubularmember that includes a plurality of pipes through which the elongatemember passes, with the tubular member and the elongate member beingshaped, in a complementary manner, to form a plurality of deformationswhich are spaced from each other in a longitudinal direction of theelongate member so that withdrawal of the elongate member from thetubular member is inhibited while providing a controlled yieldingaction; and wherein the elongate member is retained in the tubularmember only by the shaped complementary deformations which permit asliding movement of the elongated member relative to the tubular memberin the longitudinal direction after a predetermined load is exerted onthe elongate member.
 16. An anchor device according to claim 15 whereinthe deformed portion of the elongate member extends in a longitudinaldirection with a substantially sinusoidal shape.
 17. An anchor devicewhich includes a pipe, an elongate load bearing member which is partlyinside and enclosed by the pipe and which has an end which protrudesfrom the pipe, and a restraining component which is engaged with theprotruding end, and wherein the pipe and elongate member are shaped witha plurality of complementary sinusoidal deformations, along theirrespective lengths, so that the elongate member can only be withdrawnfrom the tubular member by further deforming the elongate member therebyto provide a controlled yielding action; and wherein the elongate memberis retained in the tubular member only by engagement of the sinusoidaldeformations of the elongate member and the tubular member so that arelative sliding movement of the elongated member and the tubular memberis permitted in the longitudinal direction after a predetermined load isexerted on the elongate member.
 18. An anchor device which includes atubular member, and an elongate load bearing member having one endinside the tubular member, which encloses the elongate member over aportion of the length of the elongate member, and a restrainingcomponent that is secured to an opposite end of the elongate memberextending from the tubular member and at a location that is outside thetubular member, with the tubular member and the enclosed portion of theelongate member both being deformed, in a complementary manner, at eachof a plurality of locations to form deformations which are spaced fromeach other in a longitudinal direction of the elongate member and withthe shape of the complementary deformations being such that withdrawalof the elongate member from the tubular member is inhibited to provide acontrolled yielding action; and wherein the elongate member is retainedin the tubular member only by the complementary deformations whichpermit a sliding movement of the elongated member relative to thetubular member in the longitudinal direction after a predetermined loadis exerted on the elongate member.
 19. An anchor device according toclaim 18 wherein the elongate member is selected from a rod and a cable.20. An anchor device according to claim 18 wherein the deformed portionof the elongate member extends in a longitudinal direction with asubstantially sinusoidal shape.